Some applications require the use of electrical equipment in hazardous locations where exposure to chemical, flammable and/or combustible conditions is likely. Electrical equipment used in such hazardous locations requires construction to, and compliance with, exacting standards to lessen the chance of electrical equipment malfunction and failure.
Underwriters Laboratories Inc. (UL) is an independent product safety certification organization that has been testing products and writing safety standards for over a century. Underwriters Laboratories, Inc has written safety standard UL 674 “Standard for Electric Motors and Generators for Use in Division 1 Hazardous (Classified) Locations”. Electrical equipment such as motors, generators, panels, raceways and junctions used under hazardous conditions can be constructed in accordance to the UL 674 standard. Equipment used in such conditions typically must be approved under this standard. Approval under a UL standard can require testing of the system and/or system components to ensure compliance with that UL standard.
One part of the UL 674 standard requires that openings in electrical equipment be potted or sealed with an approved material that can meet specific performance criteria for resistance to chemicals. These criteria are specified in UL standard 674, section 45. UL standard 1203, “Tests On Sealing Materials”, is similar to UL 674, section 45. This standard specifies resistance to damage and degradation of a sealant material after exposure to vapors from a number of specified chemicals. Approved sealant materials must retain at least 85% of their compressive strength after 168 hours exposure to saturated vapors in air of each of the specified chemicals and must not shrink, swell, crack or lose or gain more than 1 percent of their weight.
Most epoxy compositions will degrade substantially when exposed to one or more of the test chemical vapors and therefore can not meet the chemical resistance requirements of UL 674. Retention of at least 85% compression strength after exposure to glacial acetic acid is especially difficult for most epoxy compositions.
There are very few materials alleged to be approved for use under the UL 674 standard. One material is CHICO available from Crouse Hinds Cooper. CHICO is an inorganic cementitious material that is mixed with water and poured into a fitting or aperture to form a seal. More recently, CHICO SPEEDSEAL available from Crouse Hinds Cooper has been approved. CHICO SPEEDSEAL is believed to be polyurethane that expands during curing to form a seal in a fitting or aperture. Other useful sealants are KNEADASEAL and KNEADASEAL SL available from Polymeric Systems, Inc. of Pennsylvania, USA. KNEADASEAL is a solid epoxy putty stick that is kneaded between a user's fingers to mix and subsequently forced into a fitting or aperture to form a seal that subsequently cures. Forcing the dense, solid putty into a small aperture to form a seal is difficult, especially if wires penetrate the aperture. KNEADASEAL SL is a pourable epoxy compound. Technical literature notes that KNEADASEAL SL contains bisphenol A epoxy resins.